How to easily add cloth seam channel to a model
The easy way is to simply draw it on a bump map.  Are you doing a 1mm flyby of your foot?  Are you carefully lighting the scene for your tabi seam to catch dramatic shadows?  Unless you are, geometry is pointless, save your verts for somewhere they matter.

But I dunno, maybe you're doing a foot flyby.  The way to do it with geometry is to first fix the topo on your mesh-- you need an edge flow that follows the seams, something that is not yet present on your image.  What you want is topo where there is some edge loop that you can cleanly select that represents the seam.

Once you have that topo, it's pretty trivial.  Select your seam loop and start with a bevel-- mouse wheel up to get an extra edge loop in the center:



Ctrl numpad - to shrink your selection to only the central loop of the bevel, ctrl , to set pivot point to median, alt-s to scale along normals, scale to taste and confirm, and you have a seam.